Oxide superconducting wires are produced by the following process:                (a) a metal tube is filled with a material (material powder) of an oxide superconductor;        (b) the metal tube is processed by drawing or rolling to obtain a wire having an intended shape;        (c) the obtained wire is heat-treated to sinter the material of the oxide superconductor; and        (d) thus, an oxide superconductor is produced.        
A material of an oxide superconductor has been produced by the following method, for example: First, powders of raw materials of an oxide or carbonate of elements for constituting the oxide superconductor are mixed with a specified ratio. Next, the mixed powder is treated a plurality of times with a heat treatment at 700 to 860° C. or so and with pulverization. Thus, the material of the oxide superconductor is obtained that is composed of a superconducting phase and a non-superconducting phase. Such a method of producing a material of an oxide superconductor has been disclosed in the published Japanese patent application Tokukai 2004-119248 (Patent literature 1), for example.
However, the above-described production method has a problem in that the heat treatment and pulverization are required to perform a plurality of times in order to make the material powder uniform. In addition, even the heat treatment and pulverization are performed a plurality of times, the uniformity of the material powder has a limitation.
In view of the above-described situation, for example, non-patent literatures 1 and 2 have disclosed a production method that can easily produce a material of an oxide superconductor that has uniformly distributed elements constituting the oxide superconductor. In the production methods disclosed in non-patent literatures 1 and 2, first, the elements for constituting the oxide superconductor are dissolved in a nitric acid solution to ionize the elements. Next, the nitrate solution is sprayed in a high-temperature atmosphere to remove the solvent so that a powder can be obtained. Then, the temperature of the atmosphere is reduced to cool the powder. Thus, the material powder comprising the elements for constituting the oxide superconductor is produced.                Patent literature 1: the published Japanese patent application Tokukai 2004-119248.        Non-patent literature 1: M. Awano, et al., “Enhancement for Synthesis of Bi—Pb—Sr—Ca—Cu—O superconductor by the Spray Drying and Subsequent Calcination with Rapid Heating,” Japanese Journal of Applied Physics, Vol. 30, No. 5A, (1991), pp. L806-L808.        Non-patent literature 2: N. Tohge, et al., “Preparation Conditions and Morphology of Superconducting Fine Particles in the Bi—Ca—Sr—Cu—O System Prepared by Spray Pyrolysis,” J. Am. Ceram. Soc., 74 (9), (1991), pp. 2117-2122.        